Method and system for reducing power consumption in a rotatable media data storage device

ABSTRACT

Methods and systems in accordance with embodiments of the present invention can provide for reduced power consumption in rotatable media data storage devices. A voice coil motor driver configured to operate as a linear driver can be operated in a quasi-switch mode, for example when idle, or linear mode, for example during read/write operations and seeks, thereby achieving power savings along with accurate current control. Alternatively, a voice coil motor driver configured to operate as a switched driver can be operated at a reduced limit cycle, for example when idle, or a higher limit cycle, for example during read/write operations and seeks, thereby achieving power savings.

TECHNICAL FIELD

The present invention relates to rotatable media data storage devices,as for example magnetic or optical hard disk drive technology, and powerconsumption of rotatable media data storage devices.

BACKGROUND

Over the past few years, notebook computers have become progressivelythinner and lighter, and battery technology has improved significantly;but, though both thinner and lighter, notebook computers haveincorporated ever-more powerful CPU's, larger and higher resolutionscreens, more memory and higher capacity hard disk drives. Feature-richmodels include a number of peripherals such as high-speed CD-ROM drives,DVD drives, fax/modem capability, and a multitude of different plug-inPC cards. Each of these features and improvements creates demand forpower from system batteries. Many portable electronics, such as MP3players and personal digital assistants, now use rotatable data storagedevices as well, and by their nature and size place great demands forpower on batteries.

Many manufacturers of rotatable data storage devices reduce demand onbatteries by employing power savings schemes; for example, manymanufacturers ramp down and stop a rotating storage medium after aperiod of inactivity. This scheme comes at a cost to performance—themedium must be spun up from standstill before information can beaccessed from the medium.

BRIEF DESCRIPTION OF THE FIGURES

Further details of embodiments of the present invention are explainedwith the help of the attached drawings in which:

FIG. 1 is a control schematic of a typical hard disk drive for applyinga method in accordance with one embodiment of the present invention;

FIG. 2 is a schematic of a linear mode spindle motor driver used in thetypical hard disk drive of FIG. 1;

FIG. 3A is a schematic of a switch mode spindle motor driver used in thetypical hard disk drive of FIG. 1; and

FIG. 3B is a schematic of a pulse width modulation (PWM) controller usedin the spindle motor driver of FIG. 3A.

DETAILED DESCRIPTION

Methods and systems in accordance with embodiments of the presentinvention can provide for reduced power consumption in rotatable mediadata storage devices. FIG. 1 is a control schematic of a typical harddisk drive 100 for applying a method in accordance with one embodimentof the present invention. The hard disk drive 100 includes at least onerotatable data storage medium 102 capable of storing information on atleast one surface. Numbers of disks and surfaces can vary by hard diskdrive. In a magnetic hard disk drive as described below, the at leastone storage medium 102 is a magnetic disk. A closed loop servo systemcan include a rotary actuator having an arm 106 for positioning a head104 over selected tracks of the disk 102 for reading or writing, or formoving the head 104 to a selected track during a seek operation. In oneembodiment, the head 104 is a magnetic transducer adapted to read datafrom and write data to the disk 102. In another embodiment, the head 104includes separate read elements and write elements. The separate readelement can be a magneto-resistive head 104, also known as an MR head104. It will be understood that multiple head 104 configurations can beused.

The servo system can include a driver for driving a voice coil motor(VCM) 108 for rotating the actuator arm 106, a driver for driving aspindle motor 112 for rotating the disk(s) 102, a microprocessor 120 forcontrolling the VCM driver 108 and the spindle motor driver 112, and adisk controller 128 for receiving information from a host 122 and forcontrolling many disk functions. A host can be any device, apparatus, orsystem capable of utilizing the data storage device, such as a personalcomputer or Web server. In some embodiments, the disk controller 128 caninclude an interface controller for communicating with a host 122, whilein other embodiments a separate interface controller can be used. Themicroprocessor 120 can also include a servo controller, which can existas circuitry within the hard disk drive 100 or as an algorithm residentin the microprocessor 120, or as a combination thereof. In otherembodiments, an independent servo controller can be used. In still otherembodiments, the servo controller, VCM driver 108, and spindle motordriver 112 can be integrated into a single application specificintegrated circuit (ASIC). One of ordinary skill in the art canappreciate the different means for controlling the spindle motor and theVCM.

The microprocessor 120 can include integrated memory (such as cachememory), or the microprocessor 120 can be electrically connected withexternal memory (for example, static random access memory (SRAM) 110 oralternatively dynamic random access memory (DRAM)). The disk controller128 provides user data to a read/write channel 114, which sends signalsto a current amplifier or preamp 116 to be written to the disk(s) 102.The disk controller 128 can also send servo signals to themicroprocessor 120. A disk controller 128 can include a memorycontroller for interfacing with buffer memory 118. In one embodiment,the buffer memory 118 can be DRAM.

The microprocessor 120 can command current from the spindle motor driver112 to drive the spindle motor, thereby rotating the disk(s) 102. Acontrol structure of the spindle motor driver 112 is typicallyconfigured to operate exclusively in either linear mode or switch modeto provide the commanded current to windings of the spindle motor. Asimilar driver stage can be used for spindle motor drivers 112 havingeither a linear mode or a switch mode configuration. A pre-driver stagecontrol structure determines whether the instantaneous current is drivento a specific target (as in linear mode) or the instantaneous current isdriven in a limit cycle where the average current value is approximatelythe specific target value with controlled maximum peak current values(as in switch mode).

FIG. 2 is a simplified schematic of a portion of one example of aspindle motor driver 112 configured to operate in linear mode (hereaftercalled a linear mode driver) 212, showing exemplary elements forproviding current to the spindle windings 240 including the driver stage250, a commutation sequencer 242, an operational amplifier stage 254, acurrent feedback stage 252, and a voltage centering bias structure 256.As mentioned above, a similar driver stage 250 can be used for eitherthe linear mode driver or a spindle motor driver 112 configured tooperate in switch mode (hereafter called a switch mode driver), and inthis example is shown to comprise a MOSFET triplet “H-bridge”.Alternatively, the driver stage 250 can comprise a number of differentcomponents fabricated using a number of different manufacturingtechniques. One of ordinary skill in the art can appreciate thedifferent configurations for the driver stage.

Immediately preceding the driver stage 250 in the linear mode driver isthe current feedback stage 252 where the current in each individualMOSFET transistor 250 a-f is controlled via a current mirror controlstructure 252 a-f.

The stage preceding the current feedback stage 252 is the operationalamplifier stage 254, typically only implemented in a linear mode driver.The output of an operational amplifier 254 x-z is a signal targeting acontinuous current value. Each operational amplifier 254 x-z generates apair of voltages for each phase winding that are applied to currentmirror transistors 252 a-f in the current feedback stage 252 for controlof driver stage transistor current. The input to the operationalamplifier stage 254 can be controlled by a switch 256 associated withthe commutation sequencer 242 that typically guides the commandedcurrent signals 244 to two of the three operational amplifiers 254 x-zin the operational amplifier stage 254 to enable current flow in two ofthe three windings 240, thereby maximizing the peak positive torqueproduced by the spindle motor. The commutation sequencer 242 sequencesthrough commutation states, which can correspond to sets of torquecurves representing the functional relationship between torque, currentflow and angular position.

The voltage centering bias structure 256 is selectively multiplexed (viaa switch) to active transistor pairs (e.g. 250 a and 250 b) to centerthe output voltage of the driven windings to the power supply voltageand to keep the output impedance of the undriven transistor pair high.This balances the power dissipation in the driver stage 250 evenlybetween the upper and lower FET transistors in each transistor pair.

The schematic shown in FIG. 2 is merely one example of a schematic for alinear mode driver. A linear mode driver can include additional or fewerelements, while achieving similar results. One of ordinary skill in theart can appreciate the different configurations for achieving currentcontrol.

FIG. 3A is a simplified schematic of a portion of one example of aswitch mode driver 312, showing exemplary elements for providing powerto the spindle windings 240, including the driver stage 250, acommutation sequencer 242, a pulse width modulation (PWM) controller362, a driver controller 358, and a current feedback loop 360. Theoutput of the driver controller 358 is a state where the individualtransistors 250 a-f are either fully turned on (saturated) or fullyturned off, rather than a continuous current value.

As with the linear mode driver 212, commutation states can correspond toa set of torque curves. The commutation sequencer 242 sequences throughthe commutation states to control switching elements 250 a-f that drivethe spindle motor to maximize the peak positive torque produced by thespindle motor. The commutation sequencer 242 switches on two powertransistors 250 a-f on opposite legs of windings 240 during each of thecommutation states (via driver controller 358). Thus, there is onefloating winding for the spindle motor during each of the commutationstates.

The PWM controller 362 monitors the instantaneous current flow in thedriver stage 250 and when the current builds up to a value greater thana programmable threshold the PWM controller 362 overrides thecommutation sequencer 242 and the driver stage 250 is turned off via thedriver controller 358. In this way, the maximum current in the limitcycle profile of the spindle current is very well controlled. Maximumcurrent control is used to control the average value of the spindlecurrent, and by extension to control the speed of the spindle.

FIG. 3B illustrates in greater detail components that comprise the PWMcontroller 362. The PWM controller 362 comprises a voltage comparator364 and a one-shot timer 366. The one-shot timer 366 allows current flow368 in the spindle windings to increase at a rate limited by theinductance of the spindle winding 240. When the current 368 in thespindle winding increases above the command current threshold, thevoltage comparator 364 is tripped, setting the one-shot timer 366. Whenthe one-shot timer 366 is set, the driver stage transistors 250 a-f aredisabled, causing the current 368 in the spindle winding to drop belowthe command current threshold. When the one-shot timer 366 times out,the voltage comparator 364 has cleared (i.e. is no longer in a “tripped”state), and the process is repeated, causing a limit cycle in thespindle current with well controlled maximum current peaks. In otherembodiments, the one-shot timer 366 can control minimum current dipsrather than maximum current peaks by enabling the driver stagetransistors 250 a-f when the current drops below a minimum current dip.One of ordinary skill in the art can appreciate the different methods bywhich a limit cycle can be controlled.

In principle, a switch mode driver is a very efficient driver. Bycontinually shorting the power supply across the load, a relativelyprecise current having a saw-tooth pattern can be obtained. Typically,faster switching produces smaller saw-tooths, resulting in a smootheroverall current plot. A switch mode driver 312 having no resistancedissipates no power and all power losses are across the load (thespindle). In reality, there are some power losses associated withswitching due to resistance in the switch mode driver 312 and per-switchenergy dissipation, but typically the switch mode driver 312 dissipatesless power than a linear mode driver 212. Inaccuracies in the one-shottime value and/or noise in the current feedback signal can result insubstantial deviations in the instantaneous current values that are notrepeatable. These inaccuracies are commonly minimized in a switch modedriver 312 by switching at a very high frequency, providing moreaccurate control over the current delivered to the load but at the sametime as the frequency of switching increases, switching losses increaseand the power dissipated in the switch mode driver 312 increases.Further, electrical interference can be generated by switching,potentially interfering with the heads 104 during seeks and read/writeoperations.

The schematics shown in FIGS. 3A and B are merely examples of switchmode driver configurations. One of ordinary skill in the art canappreciate the different configurations for achieving current control.

In one embodiment, a method in accordance with the present invention canbe used to achieve power savings comparable with switch mode drivers,for example when idle, and achieve current control associated withlinear mode drivers, for example during read/write operations and seeks.The method can be applied to a hard disk drive 100 configured with alinear mode driver 212 (as shown in FIG. 2). The method comprises a lowpower mode activated when the head 104 is idle; that is, not reading orwriting to or from the medium. In a low power mode, the microprocessor120 commands a grossly exaggerated current 244 from the linear modedriver 212, saturating the operational amplifier stage 254. At some timeinterval later, the microprocessor 120 “turns off” the driver stage 250by commanding zero current from the operational amplifier stage 254. Themicroprocessor 120 alternates between saturating the operationalamplifier stage 254 and turning the driver stage 250 off at a limitcycle. When the head 104 receives a command, the hard disk drive 100returns to linear mode and the operational amplifier stage 254 iscommanded to a current for achieving a target spindle speed.

During low power mode, the linear mode driver 212 can resemble a switchmode driver 312. However, the linear mode driver 212 typically has acontinuous current feedback loop coupled to each individual outputtransistor (the current mirror stage 252) and does not include a singlecurrent feedback loop 360. The limit cycle for the linear mode driver212 can be based on a back EMF voltage detector (not shown). Themicroprocessor 120 can use timing pulses from the back EMF voltagedetector to create control signals defining the limit cycle. The limitcycle for low power mode typically provides coarser current control.Beneficially, this can result in lower power losses attributable toswitching. By applying the method, the hard disk drive can reduce thepower consumed by the spindle motor driver 112 during periods whenpossible electrical interference from changes in current and/orimprecise spindle speed control do not interfere with the operation ofthe hard disk drive 100.

A system for applying the method in accordance with one embodiment ofthe present invention can include the hard disk drive 100 describedabove including read-only memory (ROM) for storing firmware adapted togenerate commands for current from the linear mode driver 212 such thatthe linear mode driver 212 can operate in low power mode. In a run modeof operation, either the microprocessor 120 or the disk controller 128controls all of the spindle functions except the function of flaggingthe disk controller 128 to the existence of a spindle speed fault. Foroperations other than run mode (i.e. alignment, start-up, brake, and lowpower mode) the firmware is used for direct, real-time control of thespindle current. In low power mode, the firmware can receive timingpulses based on back-EMF measurements of spindle speed. The firmware canthen generate command currents for controlling spindle speed based onthe timing pulses. The ROM used to store the firmware can beprogrammable read-only memory (PROM), or electrically erasableprogrammable read-only memory (EEPROM), etc, or alternatively, thefirmware can be stored on a medium other than ROM, for example FLASHmemory.

In other embodiments, a system for applying the method in accordancewith the present invention can include an ASIC comprising a linear modedriver 212 and a spindle speed controller (not shown), wherein thespindle speed controller can modulate the current in linear mode tomaintain the spindle speed at a constant desired value without requiringcurrent commands from the microprocessor 120. As described above, thesystem can include ROM or other medium for storing firmware. In lowpower mode, the firmware creates commands for current and sends thecommands to the ASIC, overriding the spindle speed controller andactivating the low power mode described above. In still otherembodiments, the host 122 comprises the firmware and sends the commandsto the ASIC via the serial port.

In another embodiment, a method in accordance with the present inventioncan be used to achieve additional power savings with a switch modedriver 312, for example by increasing the limit cycle when idle anddecreasing the limit cycle during read and write operations, therebytargeting the need for maximum current control. The method comprises alow power mode activated when the head 104 is idle, that is, not readingor writing to or from a medium. In low power mode, a programmablethreshold for the PWM controller 362 can be increased to increase thelimit cycle, thereby reducing the switch rate of the switch mode driver312. The reduced switch rate results in lower switching losses. When thehead 104 receives a command, the programmable threshold of the PWMcontroller 362 is decreased, decreasing the limit cycle of theswitching. A system for applying the method in accordance with oneembodiment of the present invention can comprise the hard disk drive 100described above including ROM or other medium for storing firmwareadapted to reprogram the programmable threshold of the PWM controller362. In low power mode, the firmware can be used to re-program theprogrammable threshold of the PWM controller 362 so that the limit cycleis longer.

In still other embodiments, a method in accordance with the presentinvention can be used to achieve power savings in the VCM. The methodcan be applied to a hard disk drive 100 configured with a VCM driver 108operating in linear mode. In the VCM, current is provided to a singlevoice coil, and the VCM driver 108 can have a simpler structure thanthat of the linear mode driver 212 for the spindle. The method comprisesa low power mode activated when the head 104 is idle; that is, notreading or writing to or from the medium. In a low power mode, themicroprocessor 120 commands a grossly exaggerated current from the VCMdriver 108. At some time interval later, the microprocessor 120 “turnsoff” the VCM driver 108 by commanding zero current. The microprocessor120 alternates between saturating and turning off the VCM driver 108 ata limit cycle. When the head 104 receives a command, the hard disk drive100 returns to linear mode and the VCM driver 108 is commanded to acurrent to pivot the rotary actuator.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many modifications andvariations will be apparent to one of ordinary skill in the relevantarts. The embodiments were chosen and described in order to best explainthe principles of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications that are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the claims and their equivalence.

1. A method to reduce the power consumed by a data storage devicecomprising: providing a data storage device including: a rotary actuatorassembly; a voice coil motor connected with said rotary actuatorassembly; wherein the voice coil motor is electrically connected withtwo terminals; applying a first voltage potential across the twoterminals of the voice coil motor to cause the rotary actuator assemblyto move; applying a second voltage potential across the two terminals ofthe voice coil motor; repeatedly switching between applying the firstvoltage potential and the second voltage potential across two terminalsof the voice coil motor such that an approximately constant current ismaintained across two terminals of the voice coil motor.
 2. The methodof claim 1, wherein the switching is at a rate greater than 50 kHz.
 3. Aprocessor having instructions for: applying a first voltage potentialacross two terminals of a voice coil motor to cause a rotary actuatorassembly to move; applying a second voltage potential across twoterminals of the voice coil motor; repeatedly switching between applyingthe first voltage potential and the second voltage potential across twoterminals of the voice coil motor such that an approximately constantcurrent is maintained across two terminals of the voice coil motor;receiving a command to perform an operation on the at least one disk;and maintaining the first voltage potential across two terminals of thevoice coil motor.
 4. A system for storing and retrieving information,comprising: a rotatable means for storing data a positioning means forpositioning a head to store or retrieve data on said rotatable means; ameans for moving said positioning means; a means for applying a voltageto said means for moving such that said positioning means moves at adesign rate; and a means for selectively switching between a firstvoltage and a second voltage such that an approximately constant currentis delivered to said means for moving.
 5. The system of claim 4,including a means for communicating with said rotatable means, whereinthe means for communicating with said rotatable means is removed fromcommunication with said rotatable means when switching between saidfirst voltage and said second voltage.
 6. A system for storing andretrieving information, comprising: a spindle; at least one diskconnected with the spindle; a head in communication with each of said atleast one disk; a rotary actuator assembly connected with said head; avoice coil motor having at least two terminals connected with the rotaryactuator assembly for moving said head; and a power driver electricallyconnected with said voice coil motor; wherein a first voltage potentialis applied across two terminals of said voice coil motor such that saidhead moves at a design speed; wherein when said head is removed fromcommunication with said at least one disk, said power driver switchesbetween applying said first voltage potential and a second voltagepotential across two terminals such that a constant current is deliveredto said voice coil motor.
 7. The method of claim 6, wherein theswitching is at a rate greater than 50 kHz.